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# What is an isosceles triangle?

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An isosceles triangle is a specific type of triangle where only two of the side lengths and two of the internal angles are equal. There are also other types of triangles like equilateral triangles and scalene triangles.

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A triangle is a basic polygon shape with three sides. The sides must all be straight and form a closed loop. The internal angles of a triangle always add up to 180 degrees.

It is possible for all three sides of a triangle to be the same length. If they are, the angles will also be the same, with a size of 60 degrees. This is a special type of triangle called an equilateral triangle.

In addition to isosceles and equilateral triangles, there are also triangles where none of the sides or angles are the same size. These are called scalene triangles.

Triangles can also be classified according to the size of their angles. An acute triangle is one where all angles are less than 90 degrees. If a triangle has one angle that is exactly 90 degrees, it is called a right triangle, named after the right angle it contains. Finally, if a triangle has an angle over 90 degrees, it is classified as an obtuse triangle.

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## Related Questions

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A triangle can never have any parallel lines because there must be three angles that add up to 180 degrees, which makes it impossible for the three sides to avoid intersecting. A parallel line can never intersect with another, and triangles must always have intersecting sides.

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Four different methods for determining triangle congruency by examining sets of sides and angles exist: SSS (side, side, side), SAS (side, angle, side), ASA (angle, side, angle) and AAS (angle, angle, side). The hypotenuse and leg method can also determine the congruency of right triangles.

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The orthocenter is defined as the point where the altitudes of a right triangle's three inner angles meet. It is also the vertex of the right angle.